The current invention relates to a polarization separating filter, comprised of a central hollow waveguide in which two linear, orthogonally polarized waves can be propagated, where one end of the central hollow waveguide is dosed by a short circuit wall and in the vicinity of the short circuit wall, two waveguides are coupled to two opposing walls of the central hollow waveguide, in an at least approximately identical cross sectional plane extending perpendicular to this longitudinal axis of the hollow waveguide. A polarization separating filter of this kind has been disclosed by DE 31 11 106 C1, which discloses a rectangular hollow waveguide and a coaxial conductor in the same cross sectional plane are coupled to two opposing walls of a central hollow waveguide, which has a round or square cross section. The coupling of a coaxial conductor is expensive in manufacture and assembly since this requires special individual parts that must be manufactured with high precision (e.g. internal conductors, support disks, etc.). Since there are waveguide connection gates in standard uses of polarization separating filters, extra coaxial/waveguide transitions must be provided, as a result of which favorable reflection properties can only be achieved with difficulty.
The object of the invention, therefore, is to disclose a polarization separating filter of the type mentioned at the beginning, which can be manufactured as inexpensively as possible and which also has very favorable electrical properties.
The stated object is attained by virtue of the fact that the two waveguides are hollow waveguides, which are coupled at one end on opposite sides of the central hollow waveguide, where the hollow waveguides are dimensioned so that only the fundamental wave type can be propagated in the hollow waveguides and so that the two hollow waveguides are rotated relative to one another around their longitudinal axes so that the electromagnetic fields of the two hollow waveguides are oriented orthogonal to each other.
Since all of the hollow waveguides of this polarization separating filter are disposed in one plane, they can be integrated into a planar hollow waveguide circuit. The central hollow waveguide and the hollow waveguides coupled to the central hollow waveguide are produced as shells that are introduced into the bottom and top of a housing. Due to the compact design, it is also possible to manufacture the polarization separating filter completely out of one piece by forming a base body from the connecting sides of the hollow waveguide gates of the central hollow waveguide and of the hollow waveguides coupled to the sides of the central hollow waveguide.
Thus the two hollow waveguides can be coupled to the central hollow waveguide via orifices in order to produce as broad-band a coupling as possible. In the central hollow waveguide, at least one rod can be disposed in the coupling region of the two hollow waveguides.
It is useful for a separating plate to extend in the central hollow waveguide, from the short circuit wall into the coupling region of the two laterally coupled hollow waveguides, the separating plate being oriented perpendicular to the longitudinal axes of the coupled hollow waveguides. In the central hollow waveguide, at least in the coupling region of a lateral hollow waveguide, a strut can be provided in the angle between the separating plate and the short circuit wall.
In another embodiment, the lateral hollow waveguides have a rectangular cross section and the hollow waveguide, whose broad sides are oriented perpendicular to the longitudinal axis of the central hollow waveguide, is coupled to the central hollow waveguide by means of an E-plane bend, where the E-plane bend is comprised of a contour, which is provided in the central hollow waveguide and simultaneously constitutes a dividing wall that extends from the short circuit wall into the coupling plane of the two lateral hollow waveguides and is oriented perpendicular to the longitudinal axes of the laterally disposed hollow waveguides. This arrangement achieves an optimal decoupling of the two polarizations coupled via the lateral hollow waveguides.